1. Field of the Invention
This invention relates to apparatus for severing and stacking articles from a sheet of thermoplastic material in which the articles have been differentially pressure formed and more particularly to a trim press which includes relatively vertically movable trim dies which engage vertically opposite sides of a horizontally indexed sheet of thermoplastic material to trim articles from the sheet, and apparatus for receiving and vertically stacking the free falling severed articles.
2. Description of the Prior Art and Objects
Apparatus such as that disclosed in U.S. Pat. No. 3,664,791 granted to G.W. Brown on May 23, 1972, which is incorporated herein by reference, has been provided heretofore for successively delivering a heated thermoplastic sheet to a sheet heating station and then to a forming station at which opposed molds engage the sheet to differentially pressure form articles in the sheet. Apparatus, such as that disclosed in U.S. Pat. No. 4,313,358 issued to G.W. Brown on Feb. 2, 1982 and U.S. Pat. No. 4,391,171 granted to Michael Wendt on Jul. 5, 1983, which are incorporated herein by reference, have been provided for trimming articles from the plastic sheet.
These prior art trim presses include a horizontally disposed, horizontally reciprocally movable trim press which includes a pair of opposed dies which engage and clamp to horizontally opposite sides of a vertical sheet in which the articles are formed. The aforementioned patents disclose ejector mechanism for horizontally ejecting articles severed at a trim station.
The trim presses disclosed in the aforementioned patents are frequently referred to as horizontal trim presses which trim the part from the sheet, push the trimmed part into a stack, count the parts in the stack and then tip the stack 90.degree. to a conveyor for delivery to a shrink wrap machine or the like.
It is difficult to stack some articles with a conventional horizontal trim press because the parts sometimes fall over. As the parts are ejected from the prior art horizontal trim press, they are "on edge" and can tip which interferes with the stacking. It has been found, according to the present invention, that the stacking of severed articles is greatly enhanced if the trim dies are moved vertically and the sheet moved horizontally. Accordingly, it is an object of the present invention to provide a vertical trim press apparatus and method for vertically severing articles from a thermoplastic sheet which is indexed horizontally and then vertically stacking the trimmed articles.
It is another object of the present invention to provide method and apparatus for vertically severing and stacking articles differentially pressure formed in a sheet of thermoplastic material including opposed cooperating trim dies which are moved vertically into engagement with vertically opposite sides of a horizontally disposed sheet of thermoplastic material.
The problem with stacking parts ejected by a prior art horizontal trim press is exacerbated when the user wants to count articles in relatively small quantities. For example, dinner plates are frequently sold in small quantities for "over the counter" retail sales in the range of 8-25 plates per package. Because of the stacking difficulties associated with a horizontal trim press, plate manufacturers would frequently error on the side of having too many articles in a stack. This, of course, is costly. Accordingly, it is an object of the present invention to provide apparatus for severing and stacking articles from a sheet which has been differentially pressure formed in a sheet of thermoplastic material which is consistently accurate.
A further object of the present invention is to provide method and apparatus of the type described including apparatus for interrupting the vertical path of travel of a predetermined number of severed articles and accumulating them in a vertical stack at a predetermined level at a stacking station and releasing the stack for vertical free fall while concurrently accumulating additional severed articles at a slightly higher level to form a successive partial vertical stack and then releasing the partially formed stack to fall to said predetermined level where the balance of the stack is accumulated.
It has been found, according to the present invention, that the severed articles can be stacked in an accumulator including a pair of horizontally disposed bars underlying the trim dies and having vertical apertures therethrough aligned with apertures through the lower trim die. As the severed articles are received by the accumulator, they free fall onto support members which are movable between positions blocking the passage of freely falling articles and non-blocking positions. As the severed articles fall, ambient air underlying the articles laterally escapes outwardly therefrom. To allow the uninhibited free escape of air and not interfere with the free fall of severed articles, air escapement passages are provided in the accumulator bars. The stacking structure constructed according to the present invention eliminates the necessity of ejector mechanism such as that disclosed in the aforementioned patents.
Accordingly, it is a still further object of the present invention to provide vertical trim press apparatus of the type described which eliminates the necessity of ejector mechanism for ejecting articles severed at a trim station.
Yet another object of the present invention is to provide apparatus of the type described which includes an accumulator having air escapement passages which allows the severed articles to freely fall.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.